Hepatic fibrosis is the major cause of the morbidity and mortality of chronic liver diseases. It is characterized by excessive deposition of collagen fibers that interfere with organ function. Under normal conditions a balance exists between collagen production and degradation such that over-accumulation does not occur. How such regulation of collagen production is achieved is not well understood. Our preliminary data suggest that polypeptide by-products of collagen synthesis, procollagen propeptides, are involved in the regulation of procollagen synthesis at a pre-translational level. We propose to investigate propeptide pre-translational effects using in vitro model systems of hepatic fibrosis: cultured normal human fibroblasts, and primary cultures of human fibroblasts from fibrotic liver. The inhibitory activity and type specificity of exogenously added propeptides of type I and type III procollagen will be examined in terms of procollagen synthesis. Type specific procollagen mRNA levels will be measured. The active amino acid enzymatically digested fragments of propeptides. In order to determine the mechanism of action, we will study the effects of intact propeptides and propeptide fragments in nuclear run-off experiments to detect transcriptional inhibition and to determine if the effects are due to direct nuclear interaction of the propeptides. To determine the effects of propeptides on procollagen mRNA stability, pulse-chase experiments will be used to measure procollagen mRNA half-lives. This new information regarding the normal and abnormal regulation of collagen synthesis may form the basis for the development of new rational physiological therapeutic measures for a currently incurable medical condition.